Lithium secondary battery of high energy density with improved energy property

ABSTRACT

Disclosed is a high energy density lithium secondary battery including a cathode. The cathode contains, as cathode active materials, a first cathode active material having a layered structure and a second cathode active material having a spinel structure. The amount of the first cathode active material is between 40 and 100 wt % based on the total weight of the cathode active materials. The high density lithium secondary battery further comprises an anode, including crystalline graphite having a specific surface area (with respect to capacity) of 0.005 to 0.013 m 2 /mAh as an anode active material, as well as a separator.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of International ApplicationNo. PCT/KR2012/003958, filed May 18, 2012, which claims the benefit ofKorean Patent Application No. 10-2011-0048562, filed May 23, 2011, thedisclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a high energy density lithium secondarybattery having enhanced energy density characteristics. Morespecifically, the present invention relates to a high energy densitylithium secondary battery including: a cathode including, as cathodeactive materials, a first cathode active material represented by Formula1 below and having a layered structure and a second cathode activematerial represented by Formula 2 below and having a spinel structure,wherein the amount of the first cathode active material is between 40and 100 wt % based on the total weight of the cathode active materials;an anode including crystalline graphite having a specific surface area(with respect to capacity) of 0.005 to 0.013 m²/mAh as an anode activematerial; and a separator.

BACKGROUND ART

As mobile device technology continues to develop and demand thereforcontinues to increase, demand for secondary batteries as energy sourcesis rapidly increasing. In addition, secondary batteries have recentlybeen used as power sources for electric vehicles (EVs), hybrid electricvehicles (HEVs), and the like. Accordingly, research into secondarybatteries that can meet a variety of demands is underway and, inparticular, demand for lithium secondary batteries having high energydensity, high discharge voltage and high output stability is increasing.

Conventionally, a lithium cobalt composite oxide having a layeredstructure is generally used as a cathode active material of a lithiumsecondary battery. When such lithium cobalt composite oxide is used as acathode active material, however, cobalt as a main component is veryexpensive, and the layered structure thereof undergoes changes in volumeaccording to repeated intercalation and deintercalation of Li ions andcollapses when more than half of the Li ions are deintercalated. Thus,lithium secondary batteries including such cathode active materials arenot suitable for use in EVs or large capacity power storage devices interms of safety.

In addition, a battery including a lithium manganese composite oxidehaving a spinel structure is not suitable for use as an energy sourcefor EVs requiring relatively high energy density since a travel distancethereof is determined by battery electric energy.

Meanwhile, crystalline graphite is mainly used as an anode activematerial, which has a very low discharge potential of about −3 V withrespect to a standard hydrogen electrode potential, and exhibits veryreversible charge/discharge behavior due to uniaxial orientation of agraphene layer and thus has excellent cycle lifespan.

However, such crystalline graphite has poor output properties and thus asecondary battery including such anode active material is not suitablefor use as an energy source for HEVs requiring high output.

DISCLOSURE Technical Problem

The present invention aims to address the aforementioned problems of therelated art and to achieve technical goals that have long been sought.

Thus, an object of the present invention is to provide a lithiumsecondary battery that satisfies output levels required of EVs and HEVsand has enhanced energy density.

Technical Solution

In accordance with one aspect of the present invention, provided is ahigh energy density lithium secondary battery including:

a cathode including, as cathode active materials, a first cathode activematerial represented by Formula 1 below and having a layered structureand a second cathode active material represented by Formula 2 below andhaving a spinel structure, wherein the amount of the first cathodeactive material is between 40 and 100 wt % based on the total weight ofthe cathode active materials; an anode including crystalline graphitehaving a specific surface area (with respect to capacity) of 0.005 to0.013 m²/mAh as an anode active material; and a separator.Li_(x)(Ni_(v)Mn_(w)Co_(y)M_(z))O_(2-t)A_(t)  (1)

In Formula 1,

0.8<x≤1.3, 0≤v≤0.9, 0≤w≤0.9, 0≤y≤0.9, 0≤z≤0.9, x+v+w+y+z=2, and 0≤t<0.2;

M refers to at least one metal or transition metal cation having anoxidation number of +2 to +4; and A is a monovalent or divalent anion.Li_(a)Mn_(2-b)M′_(b)O_(4-c)A′_(c)  (2)

In Formula 2, 0.8<a≤1.3, 0≤b≤0.5, and 0≤c≤0.3; M′ refers to at least onemetal or transition metal cation having an oxidation number of +2 to +4;and A′ is a monovalent or divalent anion.

The crystalline graphite may be one selected from the group consistingof a first graphite having a specific surface area (with respect tocapacity) of 0.007 to 0.011 and a second graphite having a specificsurface area (with respect to capacity) of 0.005 to 0.013 or a mixturethereof. When the first graphite and the second graphite are used incombination, a mixing ratio of the first graphite to the second graphitemay be in the range of 1:9 to 9:1.

In particular, the first graphite may be surface-modified graphitehaving a powder conductivity of 100 S/cm or greater to less than 1000S/cm at a powder density of 1.4 to 1.6 g/cc and has 3R and 2H peaksdistinguishable as a rhombohedral peak of a (101) plane at 2θ=43° basedon XRD data.

In addition, the second graphite has a powder conductivity of 10 S/cm orgreater to less than 200 S/cm at a powder density of 1.4 to 1.6 g/cc andhas a 2H peak as the rhombohedral peak of the (101) plane at 2θ=43°based on XRD data. The second graphite has the same powder conductivityas that of amorphous carbon and thus provides enhanced outputcharacteristics to the lithium secondary battery. In addition, thesecond graphite has a similar internal structure to that of amorphouscarbon, thus greatly extending battery lifespan.

The amounts of the first cathode active material having a layeredstructure of Formula 1 and the second cathode active material having aspinel structure of Formula 2 may be in the range of 40 wt % to 100 wt%, in the range of 50 wt % to 90 wt % and in the range of 10 wt % to 50wt %, respectively, based on the total weight of the first and secondcathode active materials.

In a specific embodiment of the present invention, the first cathodeactive material may be a layered crystalline structure lithiumtransition metal oxide having an average particle diameter (with respectto capacity) of 0.03 to 0.1 μm/mAh and a powder conductivity of 1×10⁻³S/cm or greater to less than 10×10⁻³ S/cm at a powder density of 2.65 to2.85 g/cc.

In a particular embodiment, the first cathode active material of Formula1 may be a layered crystalline structure lithium transition metal oxidesatisfying conditions that the oxide includes mixed transition metals ofNi and Mn, an average oxidation number of the total transition metalsexcluding lithium exceeds +3, and the amount of Ni is the same orgreater than that of Mn on a molar ratio basis.

In addition, in another particular embodiment, the lithium transitionmetal oxide of Formula 1 may be Li(Ni_(0.5)Mn_(0.3)Co_(0.2))O₂ orLi(Ni_(1/3)Mn_(1/3)Co_(1/3))O₂.

In Formula 1, the transition metal such as Ni, Mn, or Co may besubstituted with a metal and/or other transition metal (M) elementshaving an oxidation number of +2 to +4. In particular, the transitionmetal may be substituted with at least one selected from the groupconsisting of Al, Mg, and Ti. In this case, a substitution amount maysatisfy the condition: 0.3≤z≤0.6.

In addition, in a specific embodiment of the present invention, thesecond cathode active material may be a spinel crystalline structurelithium transition metal oxide having an average particle diameter (withrespect to capacity) of 0.1 to 0.2 μm/mAh and a powder conductivity of1×10⁻⁵ S/cm or greater to less than 10×10⁻⁵ S/cm at a powder density of2.65 to 2.85 g/cc.

In Formula 2, M′ may be at least one selected from the group consistingof Co, Mn, Ni, Al, Mg, and Ti.

In addition, in Formulas 1 and 2, the oxygen ion may be substituted witha monovalent or divalent anion (A, A′) within a predetermined range,wherein A and A′ may be each independently at least one selected fromthe group consisting of halogens such as F, Cl, Br, and I, S, and N.

Substitution of these anions enables high binding ability with thetransition metals and structural transition of the compound isprevented, whereby the lithium secondary battery may have improvedlifespan. On the other hand, when the substitution amounts of A and A′are too high (t>0.2), the lifespan of the lithium secondary battery mayrather be deteriorated due to incomplete crystal structure.

In the cathode active material of Formula 1 or 2, when O is substitutedwith a halogen or the transition metal such as Ni, Mn, or the like issubstituted with another transition metal (M, M′), the correspondingcompound may be added prior to high-temperature reaction.

The high energy density lithium secondary battery including the cathodeand anode active materials having the aforementioned particular physicalquantities has a capacity with respect to volume of 0.05 to 0.09 Ah/cm³and an energy with respect to volume of 0.2 to 0.4 Wh/cm³. The physicalquantities may be measured using measurement methods known in the art.In particular, the specific surface area may be measured by BET, thepowder density may be measured using a true density measurement method,and the powder conductivity may be measured by measuring sheetresistance after forming a powder into a pellet.

The separator is disposed between the cathode and the anode and, as theseparator, a thin insulating film with high ion permeability and highmechanical strength is used. The separator generally has a pore diameterof 0.01 to 10 μm and a thickness of 5 to 300 μm.

As the separator, sheets or non-woven fabrics, made of an olefin polymersuch as polypropylene; or glass fibers or polyethylene, which havechemical resistance and hydrophobicity, or kraft papers are used.Examples of commercially available separators include Celgard seriessuch as Celgard® 2400 and 2300 (available from Hoechest Celanese Corp.),polypropylene separators (available from Ube Industries Ltd., or PallRAI Co.) and polyethylene series (available from Tonen or Entek).

In a specific embodiment of the present invention, the separator may bean organic-inorganic composite separator including a polyolefin-basedseparator and an inorganic material such as silicon. Prior patentapplications of the present applicant disclose the fact that theorganic-inorganic composite separator enables improved safety or thelike of lithium secondary batteries.

The present invention also provides a medium and large-scale batterymodule including the above-described high energy density lithiumsecondary battery as a unit battery and a medium and large-scale batterypack including the battery module.

In addition, the present invention provides a device using the batterypack as a power source. In particular, the battery pack may be used as apower source of electric vehicles, hybrid electric vehicles, plug-inhybrid vehicles, or power storage devices.

The configuration of the medium and large-scale battery module andbattery pack and fabrication thereof are known in the art, and thus, adetailed description thereof will be omitted here.

The cathode may be manufactured by coating, on a cathode currentcollector, a slurry prepared by mixing a cathode mixture including thecathode active material with a solvent such as NMP or the like anddrying and rolling the coated cathode current collector.

The cathode mixture may optionally include a conductive material, abinder, a filler, or the like, in addition to the cathode activematerial.

The cathode current collector is generally fabricated to a thickness of3 to 500 μm. The cathode current collector is not particularly limitedso long as it does not cause chemical changes in the fabricated lithiumsecondary battery and has high conductivity. For example, the cathodecurrent collector may be made of copper, stainless steel, aluminum,nickel, titanium, sintered carbon, copper or stainless steelsurface-treated with carbon, nickel, titanium, silver, or the like, analuminum-cadmium alloy, or the like. The cathode current collector mayhave fine irregularities at a surface thereof to increase adhesionbetween the cathode active material and the cathode current collector.In addition, the cathode current collector may be used in any of variousforms including films, sheets, foils, nets, porous structures, foams,and non-woven fabrics.

The conductive material is typically added in an amount of 1 to 30 wt %based on the total weight of the mixture including the cathode activematerial. There is no particular limit as to the conductive material, solong as it does not cause chemical changes in the fabricated battery andhas conductivity. Examples of conductive materials include graphite suchas natural or artificial graphite; carbon black such as carbon black,acetylene black, Ketjen black, channel black, furnace black, lamp black,and thermal black; conductive fibers such as carbon fibers and metallicfibers; metallic powders such as carbon fluoride powder, aluminumpowder, and nickel powder; conductive whiskers such as zinc oxide andpotassium titanate; conductive metal oxides such as titanium oxide; andpolyphenylene derivatives.

The binder is a component assisting in binding between the activematerial and the conductive material and in binding of the activematerial to the cathode current collector. The binder is typically addedin an amount of 1 to 30 wt % based on the total weight of the mixtureincluding the cathode active material. Examples of the binder include,but are not limited to, polyvinylidene fluoride, polyvinyl alcohols,carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM),sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and variouscopolymers.

The filler is optionally used as a component to inhibit cathodeexpansion. The filler is not particularly limited so long as it is afibrous material that does not cause chemical changes in the fabricatedbattery. Examples of the filler include olefin-based polymers such aspolyethylene and polypropylene; and fibrous materials such as glassfiber and carbon fiber.

As a dispersion solution, isopropyl alcohol, N-methylpyrrolidone (NMP),acetone, or the like may be used.

Uniform coating of an electrode material paste on a metallic materialmay be performed using a method selected from among known methods or anew appropriate method in consideration of properties of the electrodematerial. For example, the coating process may be performed by applyingthe paste to the cathode current collector and uniformly dispersing thepaste thereon using a doctor blade. In some embodiments, the applicationand dispersion processes may be implemented as a single process. Thecoating process may be performed by, for example, die-casting, commacoating, screen-printing, or the like. In another embodiment, the pastemay be molded on a separate substrate and then adhered to a currentcollector via pressing or lamination.

The drying of the coated paste on a metallic plate may be performed in avacuum oven at a temperature between 50 and 200° C. for a period of oneday.

The anode may be manufactured by coating the anode active material on ananode current collector and drying the coated anode current collector.As desired, components such as the above-described conductive material,binder and filler may further be optionally added to the anode activematerial.

The anode current collector is typically fabricated to a thickness of 3to 500 μm. The anode current collector is not particularly limited solong as it does not cause chemical changes in the fabricated secondarybattery and has conductivity. For example, the anode current collectormay be made of copper, stainless steel, aluminum, nickel, titanium,sintered carbon, copper or stainless steel surface-treated with carbon,nickel, titanium, or silver, aluminum-cadmium alloys, or the like. As inthe cathode current collector, the anode current collector may also havefine irregularities at a surface thereof to enhance adhesion between theanode current collector and the anode active material. In addition, theanode current collector may be used in various forms including films,sheets, foils, nets, porous structures, foams, and non-woven fabrics.

A lithium salt-containing non-aqueous electrolyte is composed of anon-aqueous electrolyte and a lithium salt. As the non-aqueouselectrolyte, a non-aqueous electrolytic solution, an organic solidelectrolyte, or an inorganic solid electrolyte may be used.

For example, the non-aqueous electrolytic solution may be an aproticorganic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate,ethylene carbonate, butylene carbonate, dimethyl carbonate, diethylcarbonate, ethyl methyl carbonate, gamma butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran,dimethylsulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethylether,formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane,methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ether, methyl propionate, or ethylpropionate.

Examples of the organic solid electrolyte include polyethylenederivatives, polyethylene oxide derivatives, polypropylene oxidederivatives, phosphoric acid ester polymers, poly agitation lysine,polyester sulfide, polyvinyl alcohols, polyvinylidene fluoride, andpolymers containing ionic dissociation groups.

Examples of the inorganic solid electrolyte include nitrides, halidesand sulfates of lithium (Li) such as Li₃N, LiI, Li₅NI₂, Li₃N—LiI—LiOH,LiSiO₄, LiSiO₄—LiI—LiOH, Li₂SiS₃, Li₄SiO₄, Li₄SiO₄—LiI—LiOH, andLi₃PO₄—Li₂S—SiS₂.

The lithium salt is a material that is readily soluble in thenon-aqueous electrolyte and examples thereof include LiCl, LiBr, LiI,LiClO₄, LiBF₄, LiB _(m)Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆,LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, LiSCN, LiC(CF₃SO₂)₃, (CF₃SO₂)₂NLi,chloroborane lithium, lower aliphatic carboxylic acid lithium, lithiumtetraphenyl borate, and imide.

In addition, in order to improve charge/discharge characteristics andflame retardancy, for example, pyridine, triethylphosphite,triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphorictriamide, nitrobenzene derivatives, sulfur, quinone imine dyes,N-substituted oxazolidinone, N,N-substituted imidazolidine, ethyleneglycol dialkyl ether, ammonium salts, pyrrole, 2-methoxy ethanol,aluminum trichloride, or the like may be added to the electrolyte. Insome cases, in order to impart incombustibility, the electrolyte mayfurther include a halogen-containing solvent such as carbontetrachloride and ethylene trifluoride. In addition, in order to improvehigh-temperature storage characteristics, the electrolyte may furtherinclude carbon dioxide gas, fluoro-ethylene carbonate (FCC), propenesultone (PRS), fluoro-propylene carbonate (FPC), or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanying drawing,in which:

FIG. 1 is a graph showing X-ray diffraction (XRD) analysis results ofsurface-modified first graphite according to the present invention ((a):XRD analysis results of the first graphite prior to surface modificationand (b): XRD analysis results of the first graphite after surfacemodification.

MODE FOR INVENTION

Now, the present invention will be described in more detail withreference to the following examples. These examples are provided onlyfor illustration of the present invention and should not be construed aslimiting the scope and spirit of the present invention.

EXAMPLE 1

A cathode active material prepared by mixingLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ having an average particle diameter (withrespect to capacity) of 0.05 μm/mAh and LiMn₂O₄ having an averageparticle diameter (with respect to capacity) of 0.14 μm/mAh in a mixingratio of 70:30, a conductive material, and a binder were prepared in aweight ratio of 89:6.0:5.0 and then were added to NMP and mixed thereinto prepare a cathode mixture. Subsequently, the cathode mixture wascoated on an Al foil having a thickness of 20 μm and rolled and dried,thereby completing fabrication of a cathode.

Similarly, graphite having a specific surface area (with respect tocapacity) of 0.009 m²/mAh, a conductive material, and a binder wereprepared in a weight ratio of 96:1.5:2.5, added to a mixer, and mixedtherein to prepare an anode mixture. Subsequently, the anode mixture wascoated on a Cu foil having a thickness of 10 μm and rolled and dried,thereby completing fabrication of an anode.

The cathode, the anode, and a carbonate electrolytic solution containing1M LiPF₆ as an electrolyte were used to manufacture a battery.

In this regard, LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ had a powder conductivityof 1.0×10⁻³ S/cm at a powder density of 2.75 g/cc, LiMn₂O₄ had a powderconductivity of 5×10⁻⁵ S/cm at a powder density of 2.80 g/cc, and thegraphite had a powder conductivity of 250 S/cm at a powder density of1.5 g/cc.

EXAMPLE 2

A battery was manufactured in the same manner as in Example 1, exceptthat the mixing ratio of LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ to LiMn₂O₄ in thecathode active material was 80:20.

EXAMPLE 3

A battery was manufactured in the same manner as in Example 1, exceptthat graphite having a specific surface area (with respect to capacity)of 0.008 m²/mAh and a powder conductivity of 90 S/cm at a powder densityof 1.5 g/cc was used instead of the graphite having a specific surfacearea (with respect to capacity) of 0.009 m²/mAh.

EXAMPLE 4

A battery was manufactured in the same manner as in Example 3, exceptthat the mixing ratio of LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ to LiMn₂O₄ in thecathode active material was 80:20.

EXAMPLE 5

A battery was manufactured in the same manner as in Example 1, exceptthat an anode active material prepared by mixing the graphite of Example1 and the graphite of Example 3 in a mixing ratio of 70:30 was used.

EXAMPLE 6

A battery was manufactured in the same manner as in Example 5, exceptthat the mixing ratio of LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ to LiMn₂O₄ in thecathode active material was 80:20.

COMPARATIVE EXAMPLE 1

A battery was manufactured in the same manner as in Example 1, exceptthat the mixing ratio of LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ to LiMn₂O₄ was30:70.

COMPARATIVE EXAMPLE 2

A battery was manufactured in the same manner as in Example 1, exceptthat a mixture of LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ having an averageparticle diameter (with respect to capacity) of 0.12 μm/mAh and LiMn₂O₄having an average particle diameter (with respect to capacity) of 0.23μm/mAh was used as the cathode active material.

COMPARATIVE EXAMPLE 3

A battery was manufactured in the same manner as in Example 1, exceptthat a mixture of LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ having a powderconductivity of 9×10⁻⁴ S/cm at a powder density of 2.75 g/cc and LiMn₂O₄having a powder conductivity of 5×10⁻⁶ S/cm at a powder density of 2.80g/cc was used as the cathode active material.

COMPARATIVE EXAMPLE 4

A battery was manufactured in the same manner as in Example 1, exceptthat graphite having a specific surface area (with respect to capacity)of 0.004 m²/mAh was used instead of the graphite having a specificsurface area (with respect to capacity) of 0.009 m²/mAh.

COMPARATIVE EXAMPLE 5

A battery was manufactured in the same manner as in Example 1, exceptthat graphite having a powder conductivity of 50 S/cm at a powderdensity of 1.5 g/cc was used instead of the graphite having a powderconductivity of 250 S/cm at a powder density of 1.5 g/cc.

EXPERIMENTAL EXAMPLE 1

Energy per unit volume of each of the batteries manufactured accordingto Examples 1 to 6 and Comparative Examples 1 to 5 was measured andmeasurement results were compared. Charging and discharging wereperformed between 3.0 and 4.2 V, and charging was measured at a constantcurrent and a constant voltage (CC/CV) and discharging was measured atCC. In the case of C-rates of the batteries, an energy of 3C wasmeasured under the condition of 1C (13A).

TABLE 1 Relative comparison between energies Vs. Example 1 (%) Example 1100 Example 2 104.4 Example 3 98.9 Example 4 103.6 Example 5 101.8Example 6 102.3 Comparative Example 1 92.3 Comparative Example 2 93.1Comparative Example 3 94.2 Comparative Example 4 93.2 ComparativeExample 5 92.7

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

INDUSTRIAL APPLICABILITY

As described above, a lithium secondary battery according to the presentinvention uses, as anode active materials, a first graphite exhibiting aparticular XRD peak and/or a second graphite exhibiting the same powderconductivity as that of amorphous carbon and uses, as a cathode activematerial well balanced with the anode active materials, a mixture of alayered-structure lithium transition metal oxide and a spinel-structurelithium manganese oxide in a predetermined ratio, whereby the lithiumsecondary battery achieves output characteristics well suited toelectric vehicles, and the like and also exhibits enhanced energydensity characteristics.

The invention claimed is:
 1. A high energy density lithium secondary battery comprising: a cathode comprising, as cathode active materials, a first cathode active material represented by Formula (1) Li_(x)(Ni_(v)Mn_(w)Co_(y)M_(z))O₂  (1) wherein 0.8<x≤1.3, 0≤v≤0.9, 0≤w≤0.9, 0≤y≤0.9, 0≤z≤0.9, and x+v+w+y+z=2; M refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and having a layered structure, and a second cathode active material represented by Formula (2) Li_(a)Mn_(2-b)M′_(b)O₄  (2) wherein 0.8<a≤1.3 and 0≤b≤0.5; M′ refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and having a spinel structure, wherein an amount of the first cathode active material is between 40 and 90 wt % based on a total weight of the first and second cathode active materials, wherein the first cathode active material has an average particle diameter with respect to capacity of 0.03 to 0.1 μm/mAh, and has a powder conductivity of 1×10⁻³ S/cm or greater to less than 10×10⁻³ S/cm at a powder density of 2.65 to 2.85 g/cc, and wherein the second cathode active material has an average particle diameter with respect to capacity of 0.1 to 0.2 μm/mAh, and has a powder conductivity of 1×10⁻⁵ S/cm or greater to less than 10×10⁻⁵ S/cm at a powder density of 2.65 to 2.85 g/cc; an anode comprising an anode active material, the anode active material comprising crystalline graphite, wherein the crystalline graphite comprises a mixture of a first graphite and a second graphite, wherein the total weight of the first graphite and the second graphite is the total weight of the anode active material, wherein the first graphite having a specific surface area with respect to capacity of 0.007 to 0.011 m²/mAh, and having a powder conductivity of 250 S/cm to less than 1000 S/cm at a powder density of 1.4 to 1.6 g/cc, and wherein the second graphite having a specific surface area with respect to capacity of 0.005 to 0.013 m²/mAh, and having a powder conductivity of 10 S/cm or greater to 90 S/cm at a powder density of 1.4 to 1.6 g/cc.
 2. The high energy density lithium secondary battery according to claim 1, wherein the first graphite is a surface-modified graphite and has 3R and 2H peaks distinguishable as a rhombohedral peak of a (101) plane at 2θ=43° based on XRD data.
 3. The high energy density lithium secondary battery according to claim 1, wherein the second graphite has a 2H peak as a rhombohedral peak of a (101) plane at 2θ=43° based on XRD data.
 4. The high energy density lithium secondary battery according to claim 1, wherein, in the Formula (1), M is at least one selected from the group consisting of Al, Mg, and Ti and, in the Formula (2), M′ is at least one selected from the group consisting of Co, Mn, Ni, Al, Mg, and Ti.
 5. The high energy density lithium secondary battery according to claim 1, wherein the lithium secondary battery has a capacity with respect to volume of 0.05 to 0.09 Ah/cm³ and an energy with respect to volume of 0.2 to 0.4 Wh/cm³.
 6. The high energy density lithium secondary battery according to claim 1, wherein the separator is an organic-inorganic composite separator.
 7. A battery module comprising the lithium secondary battery of claim
 1. 8. An electric vehicle or hybrid electric vehicle comprising the battery module of claim
 7. 9. A power storage device comprising the battery module of claim
 7. 10. The high energy density lithium secondary battery according to claim 1, wherein an amount of the first graphite is between 10 to 90 wt % based on a total weight of the first and second graphite.
 11. The high energy density lithium secondary battery according to claim 1, wherein an amount of the first graphite is between 70 to 90 wt % based on a total weight of the first and second graphite.
 12. The high energy density lithium secondary battery according to claim 1, wherein an amount of the first graphite is between 50 to 90 wt % based on a total weight of the first and second graphite. 